Thermoacoustic thermomagnetic generator

ABSTRACT

The present invention is a thermoacoustic thermomagnetic generator  100 . The generator includes a stator  5  that supports and channels magnetic fields. It further includes a magnetic field generator  2  that magnetically couples to the stator. In addition, the generator includes a magnetic circuit opening and closing member  1  that changes magnetic states in response to changes in temperature where the member couples to the stator to complete a magnetic circuit. Further, the generator includes a thermal insulator  4  that couples to the stator and the magnetic circuit opening and closing member. And, the generator includes a plurality of induction windings  3  that conduct electric current where the induction windings couple to the stator. The periodic opening and closing of the magnetic circuit creates a magnetic field in the stator that induces an alternating electric current in the induction windings which allows the generator to produce electric power.

CROSS REFERNECE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/908,711, filed May 24, 2005, which is incorporated by reference forall purposes into this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to thermoacoustic generators. Morespecifically, the present invention relates to thermoacousticthermomagnetic generators.

2. Description of the Related Art

The first record known of a thermo-magnetic motor making use of theCurie point property of materials is the Nikola Tesla patent, U.S. Pat.No. 396,121. In his patent, Dr. Tesla describes a kinematicthermo-magnetic motor in which a mechanism is caused to reciprocate bymeans of interrupting a magnetic circuit by the periodic application ofheat to a metal “keeper” component that completes the magnetic circuit.The application of heat causes the keeper to transition between magneticand non-magnetic states, and temporarily lose its ability to conductmagnetic lines of force, thereby opening the magnetic circuit. When theheat is removed the keeper cools below the Curie point transitiontemperature and returns to a ferromagnetic state, and the magneticcircuit is re-established.

The material property that facilitates this application is known todayas the Curie point of the material. It is the temperature at which agiven ferromagnetic element or composition of matter, usually a metalalloy, transitions from a ferromagnetic state to an austenitic ornon-magnetic state. By periodically heating and cooling the keeper andcausing the keeper to periodically change states, by increasing anddecreasing its temperature above and below the Curie point, Dr. Teslacreated a fluctuating magnetic field that alternately attracted andreleased a mechanical armature and produced a reciprocating motoraction.

The thermomagnetic, or pyromagnetic, Curie point property of materialsis also described in U.S. Pat. No. 5,714,829 by Guruprasad, which usesthe property in an inverse way from this invention in that magneticfields developing and collapsing in a pyromagnetic material alsogenerate thermal energy, and by means of this property such alloys canbe made to pump heat. In Guruprasad's invention, this effect is used forrefrigeration.

While ferromagnetism is generally a property of metallic materials,there are exceptions. Some organic materials such as isotopes ofgraphite and carbon have been known to exhibit ferromagnetic properties.Tatiana Makarova, a Russian scientist working at Umeå University inSweden, discovered that a polymerized isotope of carbon will exhibitferromagnetic properties above room temperature. She was experimentingwith buckyballs, isotopic carbon C60, searching for superconductingproperties. By heating and compressing the carbon molecules, she forcedthem to join together in polymeric layers. To her surprise, she foundthat the new material was magnetic even above 200° C. Prior to herdiscovery, the highest known temperature at which a non-metallicmaterial was magnetic was−255° C. This record was held by a differentmolecular form of carbon. Dr. Makarova's work is documented in thearticle: TATIANA L. MAKAROVA, BERTIL SUNDQVIST, ROLAND HOHN!, PABLOESQUINAZI, YAKOV KOPELEVICH, PETER SCHARFF, VALERII A. DAVYDOV, LUDMILAS. KASHEVAROVA, ALEKSANDRA V. RAKHMANINA, “Magnetic Carbon”, issue 413of Nature, 2001, pps. 716-718.

Other documented research on non-metallic magnetic materials can also befound in the article FERNANDO PALACIO, “A Magnet Made From Carbon”,issue 413 of Nature, 2001, pps. 690-691, which states that experimentswith nanostructured forms of graphite may have superconducting andferromagnetic properties, also above room temperature.

The NASA-Ames Laboratory also reports a rapidly expanding field withinnanomagnetism called “single magnetic molecules”. Their research hasinvolved compounds synthesized as crystalline samples composed ofidentical molecular units. In these compounds, intramolecular magneticinteractions greatly exceed those between molecules, and macroscopicmeasurements reflect the magnetic properties of an individual magneticmolecule.

Organic magnets could be important because they are much lighter thanmetals, and can also be made flexible and transparent. The study ofmagnetic molecules and nanoscale magnets may lead to non-metallicmagnetic materials that can be used to build lighter motors andgenerators.

It should be noted that the Néel temperature, TN, is the temperature atwhich a ferromagnetic or anti-ferromagnetic material becomesparamagnetic—that is, the thermal energy becomes large enough to upsetthe magnetic ordering within the material. This is analogous to theCurie point in ferromagnetic materials, and may be important inconstructing thermomagnetic generators and refrigerators fromnon-metallic materials such as carbon-based materials.

The present invention differs from Tesla and Guruprasad in that itapplies the thermomagnetic Curie point property of materials,alternately called the thermomagnetic or pyromagnetic property, tocreate an induction generator with no moving parts. In the presentinvention, the periodic application of heat to a thermomagneticmaterial, preferably a metal alloy though other thermomagnetic materialscould be used, in order to periodically open and close a magneticcircuit, is accomplished by means of a thermoacoustic wave traingenerated by a thermoacoustic engine.

The operation of one example of a thermoacoustic engine is described inU.S. Pat. No. 6,385,972 (The Thermoacoustic Resonator Patent) and inU.S. Pat. No. 6,910,332 (The Thermoacoustic Engine Patent), both patentshave a common inventor to the present invention. These patents describean electromagnetic generator that is actuated dynamically by theoscillating pressure gradient in the thermoacoustic wave. In other wordsthe armature of the generator is caused to reciprocate by theoscillating thermoacoustic wave-train, like a piston in a pneumaticmotor. The present invention, however, describes a solid state,non-dynamic thermoacoustic thermomagnetic generator in which theelectromagnetic field flux is caused to fluctuate, to be interrupted andre-established periodically, by the oscillating thermal gradient in thethermoacoustic wave-train. Thus, the generator of the present inventionhas no armature, and no moving dynamic parts.

The ability of acoustic waves propagating in an elastic working fluid totransport thermal energy is well established in the physical sciences,and thermoacoustic engines and various methodologies for making them arewell documented. In this instance the term “thermoacoustic” is used todescribe an acoustic wave transporting thermal energy. Typically, allthermoacoustic engines have some components in common, such as anelastic working fluid, hot and cold heat exchangers, etc., though thesecomponents may differ in design and operating characteristics. By meansof the present invention, the more practical form of electrical energy,derived from the less practical thermal energy, can then be used topower a wide variety of useful equipment.

The present invention uses the thermal gradient in thermoacoustic wavesto periodically raise the temperature of a thermomagnetic material pastits Curie point so that it alternates between magnetic and non-magneticstates. In conjunction with a stator, induction windings and magnet, themetal alloy forms a magnetic circuit that is periodically interruptedand re-established by the action of the thermoacoustic waves. Theexpanding and collapsing magnetic field induces an alternating currentin the stator windings. The resultant generator has no moving parts.This invention can be used in a thermoacoustic engine with hot and coldheat exchangers, a working fluid contained in a reservoir that isdivided into hot and cold zones, and a resonant waveguide that aretypical of the art of thermoacoustic engine. The basic arrangement ofcomponents of the present invention can be scaled in size from themicro-miniature to the very large. The present invention can also bearrayed in a thermoacoustic engine that contain multiple units of thepresent invention and includes a common waveguide, housing and hot andcold heat exchanger, such as in a panel array of multiple miniatureunits.

SUMMARY OF THE INVENTION

The present invention is a thermoacoustic thermomagnetic generator. Thegenerator comprises a stator that supports and channels magnetic fields.It further comprises a magnetic field generator that magneticallycouples to the stator. In addition, the generator includes a magneticcircuit opening and closing member that changes magnetic states inresponse to changes in temperature where the member couples to thestator to complete a magnetic circuit. Further, the generator includes athermal insulator that couples to the stator and the magnetic circuitopening and closing member. And, the generator includes a plurality ofinduction windings that conduct electric current where the inductionwindings couple to the stator. The periodic opening and closing of themagnetic circuit creates a magnetic field in the stator that induces analternating electric current in the induction windings which allows thegenerator to produce electric power.

In addition, the magnetic circuit opening and closing member furthercomprises a thermomagnetic or pyromagnetic material that changes statefrom a ferromagnetic condition to an austenitic non-magnetic conditionwhen its temperature is periodically increased past its Curie Pointtemperature by the thermal energy transported by the thermoacousticwaves impinging upon it.

DESCRIPTION OF THE DRAWINGS

To further aid in understanding the invention, the attached drawingshelp illustrate specific features of the invention and the following isa brief description of the attached drawings:

FIG. 1 is a cross-sectional view of the present invention showing thecomponent parts.

FIG. 2 is a cross-sectional view of the present invention housed withinan exemplary thermoacoustic engine.

FIG. 3 is a cross-sectional view of a panel array of multiple units ofthe present invention housed in a second exemplary thermoacoustic enginethat features a common waveguide, housing, cold-side heat exchanger andinsulators.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a method and apparatus for a thermoacousticthermomagnetic generator. This disclosure describes numerous specificdetails in order to provide a thorough understanding of the presentinvention. One skilled in the art will appreciate that one may practicethe present invention without these specific details. Additionally, thisdisclosure does not describe some well known items in detail in ordernot to obscure the present invention.

The present invention is a major operational component of athermoacoustic engine such as describe in the Thermoacoustic ResonatorPatent and the Thermoacoustic Engine Patent. To fully appreciate thenovelty of the present invention, I make reference to the operation ofthe present invention as used in an exemplary thermoacoustic engine aspreviously described and illustrated in those patents. A thermoacousticengine generates an acoustic wave that transports thermal energy. Thereis a thermal gradient between the nodes and antinodes of the acousticwave. As these nodes and antinodes alternately impinge upon the magneticfield opening and closing member, they impart pulses of thermal energyto it. Through this operation, the present invention is able to use thethermoacoustic waves to periodically raise the temperature of themagnetic field opening and closing member past its Curie point so thatit alternates between magnetic and non-magnetic states.

In conjunction with a stator and magnetic field generator, the magneticfield opening and closing member forms a magnetic circuit in which themagnetic lines of force are periodically interrupted and re-establishedby the action of the nodes and antinodes of the thermoacoustic wavespassing over the magnetic circuit opening and closing member. Theexpanding and collapsing magnetic field created thereby induces analternating current in the inductive windings that are coupled to thestator. As a result of the synergy between its component members, thepresent invention has no moving electromechanical parts. In addition, itis also appropriate to describe the present invention as a solid state,that is to say a non-kinetic, electromagnetic induction generator.

The stator of the present invention is preferably comprised offerromagnetic steel laminates such as is common to electric motors andgenerators, though future materials may also be applicable. In addition,the magnetic field generator may be comprised of either permanentmagnets, which are the preferred embodiment, or electric currentcarrying coils which create a magnetic field when energized. Further,the induction windings are comprised of electric current carrying wiresin which electric current flows when induced to do so by a changingmagnetic field, and are so disposed as to be affected by the fluctuatingmagnetic fields generated in the stator by the magnetic field generatorand the magnetic circuit opening and closing member. Further, themagnetic circuit opening and closing member is preferably comprised of athermomagnetic metal alloy, though non-metal materials that exhibit theability to transition between magnetic and non-magnetic states as acondition of temperature may also be used. The Curie point is thetemperature at which this transition, or change of state, takes place.

The magnetic field generator is so disposed that the magnetic fieldgenerated by it permeates the stator and the magnetic circuit openingand closing member, and these three components together complete amagnetic circuit that can be visualized as a closed loop of magneticlines of force. When the magnetic circuit opening and closing member isin a ferromagnetic state the magnetic circuit is complete and a staticmagnetic field exists within the stator. When the temperature amplitudeof the magnetic circuit opening and closing member changes sufficientlyso that the Curie Point is exceeded and the magnetic circuit opening andclosing member changes state and becomes non-magnetic, the magneticcircuit is opened, or interrupted, and the magnetic field within thestator collapses, and in so doing generates an electric current in theinduction windings. When the temperature amplitude of the magneticcircuit opening and closing member changes again in the oppositedirection, falling below the Curie point temperature of the material,the magnetic circuit opening and closing member reverts to its formerstate and becomes ferromagnetic, thereby re-closing the magnetic circuitand re-establishing the magnetic field in the stator. The magneticfield, in the course of being regenerated, expands across the turns ofthe induction windings and induces a current of opposite polarity to thefirst current. By periodically changing the temperature amplitude of themagnetic circuit opening and closing member so that the magnetic circuitopening and closing member repeatedly transitions from magnetic tonon-magnetic and back again, an alternating electric current can begenerated in the induction windings.

The magnetic circuit opening and closing member is so disposed that aportion extends through a thermal insulator, such as a ceramic baffle,which separates the stator and other components comprising the presentinvention from the waveguide in a thermoacoustic engine and thethermoacoustic wave, so that the magnetic field generator, the stator,and the induction coils are maintained at a cooler temperature than thatof the waveguide. The portion of the magnetic circuit opening andclosing member that extends through the thermal insulator and is exposedto the thermoacoustic wave, is disposed inside the waveguide hot-sideheat exchanger section of the thermoacoustic engine containing anelastic working fluid. The working fluid is maintained at a temperatureamplitude below the transitional state, or Curie Point, of the magneticcircuit opening and closing member.

With reference to FIG. 1, the thermoacoustic thermomagnetic generator100 comprises the magnetic circuit opening and closing member 1 that infixed contact with the stator 5 and completes the magnetic circuit pathwith the poles of the magnetic field generator 2. The thermal insulator4 is formed around the ends of the stator 5 and the magnetic circuitopening and closing member 1 near where they are joined. The inductionwindings 3 are wound around the stator pole piece. The thermoacousticwaves 6 impinge upon the magnetic circuit opening and closing member 1,periodically heating it past its Curie point and opening the magneticcircuit so that the magnetic field collapses and induces an electriccurrent in the induction windings 3. The magnetic circuit opening andclosing member 1 cools during the period between the thermoacousticwaves 6 and re-establishes the magnetic field. The expanding field againinduces an electric current in the induction windings 3, in the oppositedirection of the first electric current. This action continues for aslong as the thermoacoustic engine is generating thermoacoustic waves ofthe proper thermal amplitude and frequency. Thus, alternating electriccurrent is induced into the induction windings 3.

FIG. 2 is a cross-sectional view of an exemplary thermoacoustic enginethat uses the thermoacoustic thermomagnetic generator of the presentinvention. Thermal energy 9 enters the waveguide 7 via conduction froman external source and heats the working fluid contained within thewaveguide 7. Thermoacoustic waves 6 periodically traverse the workingfluid within the heated waveguide 7 and are amplified in both pressureand thermal gradient. The periodic thermoacoustic waves 6 impinge uponthe magnetic circuit opening and closing member 1 and periodicallyincrease its temperature above its Curie point, thereby interrupting themagnetic circuit in the stator 5, causing the magnetic field to collapseand inducing an electric current in the induction winding 3. The thermalinsulator 4 separates the waveguide 7 and the generator housing 8 intorespective hot and cool zones and reduces the quantity of heat from thewaveguide 7 entering into the cooler portion of the housing 8 where themagnetic field generator 2, the induction windings 3 and the stator 5reside. The thermoacoustic wave 6 periodically produces a pressuredifferential between the hot zone of the generator housing 8 adjacent tothe waveguide 7, and the cold zone of the generator housing 8 on theopposite side of the thermal insulator 4 where the magnetic fieldgenerator 2 resides. The pressure differential is periodically equalizedby the working fluid flowing from the waveguide 7 (which is also the hotside heat exchanger) hot zone side of the generator housing 8, through acheck valve not shown, into a cold side heat exchanger 10, where theworking fluid is cooled and returned back to the cold zone of the enginehousing 8 where the magnetic field generator 2 resides. The coolerworking fluid is periodically scavenged from the cold zone of thegenerator housing 8 by a thermoacoustic wave generator 11 and injectedback into the waveguide 7 hot zone where thermal expansion of theinjected working fluid produces periodic thermoacoustic waves 6.

FIG. 3 shows a cross-sectional view of another exemplary thermoacousticengine that has an engine housing 80 configured into a panel array ofmultiple generator units, of the present invention. Each thermoacousticthermomagnetic generator is so disposed that the magnetic circuitopening and closing member 1 penetrates through a common thermalinsulator 4 which divides the housing 80 into a hot zone and a coldzone, and separates the magnetic field generator 2 and other generatorcomponents in the cold zone from the common waveguide cavity 70 hotzone. The waveguide 70 (also the hot side heat exchanger) contains anelastic working fluid in which acoustic waves 6 are caused to propagate.The acoustic waves 6 are heated via conduction through the wall of thewaveguide 70 from an external source 9. The acoustic waves 6 convey heatto the magnetic circuit opening and closing member 1, periodicallyincreasing their temperature above the Curie point and thereby causing amagnetic flux to produce alternating electric current in the inductionwindings 3. The thermoacoustic wave 6 periodically produces a pressuredifferential between the waveguide 70 hot zone of the engine housing 80and the cold zone of the engine housing 80, with the hot zone and thecold zone being disposed on opposing sides of the thermal insulator 4.The pressure differential is periodically equalized by the working fluidflowing from the waveguide 70 hot zone side of the engine housing 80,through a check valve not shown, into the cold side heat exchanger 10,where the working fluid is cooled and returned back to the cold zone ofthe engine housing 8. The cooler working fluid is periodically scavengedfrom the cold zone of the generator housing 8 by a thermoacoustic wavegenerator 11 and injected back into the waveguide 70 hot zone wherethermal expansion of the injected working fluid produces periodicthermoacoustic waves 6.

To summarize, the present invention is a thermoacoustic thermomagneticgenerator. The generator comprises a stator that supports and channelsmagnetic fields. It further comprises a magnetic field generator thatmagnetically couples to the stator. In addition, the generator includesa magnetic circuit opening and closing member that changes magneticstates in response to changes in temperature where the member couples tothe stator to complete a magnetic circuit. Further, the generatorincludes a thermal insulator that couples to the stator and the magneticcircuit opening and closing member. And, the generator includes aplurality of induction windings that conduct electric current where theinduction windings couple to the stator. The periodic opening andclosing of the magnetic circuit creates a magnetic flux in the statorthat induces an alternating electric current in the induction windingswhich allows the generator to produce electric power.

In addition, the magnetic circuit opening and closing member furthercomprises a thermomagnetic or pyromagnetic material that changes statefrom a ferromagnetic condition to an austenitic non-magnetic conditionwhen its temperature is periodically increased past its Curie Pointtemperature by the thermal energy transported by the thermoacousticwaves impinging upon it.

Other embodiments of the present invention will be apparent to thoseskilled in the art after considering this disclosure or practicing thedisclosed invention. The specification and examples above are exemplaryonly, with the true scope of the present invention being determined bythe following claims.

1. A thermoacoustic thermomagnetic generator, comprising: a stator thatsupports and channels magnetic fields; a magnetic field generator thatmagnetically couples to said stator; a magnetic circuit opening andclosing member that changes magnetic states in response to changes intemperature, said member couples to said stator to complete a magneticcircuit; a thermal insulator that couples to said stator and saidmagnetic circuit opening and closing member; a plurality of inductionwindings that conduct electric current, said induction windings coupleto said stator; and wherein the periodic opening and closing of saidmagnetic circuit creates a magnetic field in said stator that induces analternating electric current in said induction windings.
 2. The claim ofclaim 1 wherein said magnetic circuit opening and closing member furthercomprises a thermomagnetic or pyromagnetic material that changes statefrom a ferromagnetic condition to an austenitic non-magnetic conditionwhen its temperature is periodically increased past its Curie Pointtemperature by the thermal energy transported by the thermoacousticwaves impinging upon it.
 3. A method to manufacture a thermoacousticthermomagnetic generator, comprising: providing a stator that supportsand channels magnetic fields; magnetically coupling a magnetic fieldgenerator to said stator; coupling a magnetic circuit opening andclosing member to said stator to complete a magnetic circuit, saidmember changes magnetic states in response to changes in temperature;coupling a thermal insulator to said stator and said magnetic circuitopening and closing member; coupling a plurality of induction windingsto said stator, said induction windings conduct electric current; andwherein the periodic opening and closing of said magnetic circuitcreates a magnetic field in said stator that induces an alternatingelectric current in said induction windings.
 4. The claim of claim 3wherein said magnetic circuit opening and closing member furthercomprises a thermomagnetic or pyromagnetic material that changes statefrom a ferromagnetic condition to an austenitic non-magnetic conditionwhen its temperature is periodically increased past its Curie Pointtemperature by the thermal energy transported by the thermoacousticwaves impinging upon it.
 5. A method to use a thermoacousticthermomagnetic generator, comprising: providing a stator that supportsand channels magnetic fields, said stator magnetically couples to amagnetic field generator, said stator couples to a magnetic circuitopening and closing member that changes magnetic states in response tochanges in temperature which completes a magnetic circuit, said statorand said member further couple to a thermal insulator, said statorfurther couples to a plurality of induction windings that conductelectric current; periodically opening and closing said magnetic circuitcreates a magnetic field in said stator that induces an alternatingelectric current in said induction windings.
 6. The claim of claim 5wherein said magnetic circuit opening and closing member furthercomprises a thermomagnetic or pyromagnetic material that changes statefrom a ferromagnetic condition to an austenitic non-magnetic conditionwhen its temperature is periodically increased past its Curie Pointtemperature by the thermal energy transported by the thermoacousticwaves impinging upon it.